Methods and devices operating with fine timing reference signals transmitted occasionally

ABSTRACT

Methods and devices enable a fine synchronization related to a data transmission on a physical channel. A fine timing reference signal is occasionally transmitted to the data transmission recipient using one of time-frequency resources in a recipient-specific pattern.

TECHNICAL FIELD

Embodiments of the subject matter disclosed herein generally relate tofine time synchronization in a wireless communication network, and, moreparticularly, to occasionally transmitting a fine timing referencesignal (FTRS) in a manner specific to a targeted recipient.

BACKGROUND

A prerequisite for a terminal to communicate with a network is toacquire time synchronization. Wideband reference signals are currentlyused for efficient and accurate time synchronization. In LTE (i.e.,Long-Term Evolution, which is a mobile communication standard), widebandCell-specific Reference Signals (CRS) are transmitted over all thesystem's bandwidth (BW), multiple times in every subframe. The CRS beingtransmitted over all the system's BW makes it difficult to introduce newchannels and signals in the future, and transmitting CRS continuouslyleads to high network energy consumption.

It is desirable to improve the methods related to timing referencesignal to enhance synchronization as needed while allowing more BWflexibility and using less energy than the conventional methodscurrently achieve.

SUMMARY

In various embodiments described in this document, a fine timingreference signal (FTRS) is transmitted when necessary (e.g., related toa data transmission on a physical channel), in a manner related to atargeted recipient. The FTRS may be transmitted in a time-frequencyresource of an FTRS pattern that is quasi-co-located (in time, infrequency or in both time and frequency) with the data transmission forwhich the accurate timing is necessary. FTRS transmission may betriggered by the targeted recipient (i.e., FTRS are transmitted ondemand), by a situation inferred from the targeted recipient's signalquality report, by the transmitting node depending on a type oftransmission on the corresponding physical channel (e.g. transmissionwith higher-order modulation or MIMO) or by an analysis of the targetedrecipient's uplink transmissions. The FTRS pattern is configurable andpreferably spans less than the entire available bandwidth.

According to an embodiment there is a method implemented in a wirelessdevice connected to a communication network. The method includeslistening according to an FTRS pattern that includes a sequence oftime-frequency resources, until detecting an FTRS related to a datatransmission on a physical channel. The method further includesreceiving the data transmission on the physical channel.

According to another embodiment there is a wireless device connectableto a communication network including a transceiver and at least oneprocessor. The transceiver is configured to listen for an FTRS relatedto a data transmission on a physical channel, and to receive the datatransmission. The at least one processor is configured to control thetransceiver to listen for the FTRS according to an FTRS pattern thatincludes a group of time-frequency resources, until the FTRS isdetected, and to decode the data transmission.

According to yet another embodiment, there is a wireless device in acommunication network having a listening module and a data receivingmodule. The listening module listens according to an FTRS pattern thatincludes a group of time-frequency resources, until detecting an FTRSrelated to a data transmission on a physical channel. The data receivingmodule receives the data transmission.

According to another embodiment, there is a method implemented in anetwork device of a communication network. The method includes detectinga trigger for transmitting an FTRS related to a data transmission on aphysical channel, for a wireless device, and transmitting the FTRSaccording to an FTRS pattern associated with the wireless device andincluding a sequence of time-frequency resources.

According to another embodiment, there is a network device of acommunication network having at least one processor and a transceiver.The processor is configured to detect a trigger for transmitting an FTRSrelated to a data transmission on a physical channel. The transceiver isconnected to and controlled by the at least one processor to transmitthe FTRS according to an FTRS pattern that includes a group oftime-frequency resources.

According to yet another embodiment, a network device in a communicationnetwork includes a detecting module and a transmission module. Thedetecting module detects a trigger for transmitting an FTRS related to adata transmission to a wireless device, on a physical channel. Thetransmission module transmits the FTRS according to an FTRS patternassociated with the wireless device and including a group oftime-frequency resources.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate one or more embodiments and,together with the description, explain these embodiments. In thedrawings:

FIGS. 1 and 2 are graphical illustrations of FTRS-related resource-usagesituations according to exemplary embodiments;

FIG. 3 is a flowchart of a method performed by a network node accordingto an embodiment;

FIG. 4 is a diagram of a method for a network node according to anotherembodiment;

FIG. 5 is a block diagram of a network node configured to performvarious methods according to an embodiment;

FIG. 6 is another diagram of a network node according to an embodiment;

FIG. 7 is a flowchart of a method performed by a wireless deviceaccording to another embodiment;

FIG. 8 is a diagram of a method for a wireless device according toanother embodiment;

FIG. 9 is a block diagram of a wireless device configured to performvarious methods according to an embodiment; and

FIG. 10 is another diagram of a wireless device according to anotherembodiment.

DETAILED DESCRIPTION

The following description of the embodiments refers to the accompanyingdrawings. The same reference numbers in different drawings identify thesame or similar elements. The following detailed description does notlimit the invention. Instead, the scope of the invention is defined bythe appended claims. The following embodiments refer to methods,wireless devices and nodes in a communication network.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with an embodiment is included in at least oneembodiment of the subject matter disclosed. Thus, the appearance of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout the specification is not necessarily referring to the sameembodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

The following abbreviations are used in this document:

CDM Code Division Multiplex

CRS Cell-specific Reference Signal

FTRS Fine Timing Reference Signal

HOM Higher Order Modulation

LTE Long-Term Evolution

MIMO Multiple Input Multiple Output

RRC Radio Resource Control

3GPP, the standardization organization behind LTE, has begun work on 5G,a new generation of communication standards. 5G will consist of LTEevolution together with a new radio-access technology, known as “NR”.LTE aspect in related to backwards-compatible enhancements in theexisting spectrum up to ˜6 GHz, while NR focuses on existing and newspectrum. Although large amounts of contiguous spectrum are lesscumbersome to find at higher frequencies, lower frequencies areimportant for wide-area coverage. NX will, therefore, be able to operatefrom below 1 GHz up to close to 100 GHz.

In 5G, the time-synchronization procedure is planned to have two phases.A wireless device achieves coarse time synchronization in the firstphase and determines the start of the downlink transmission frame. Thiscoarse synchronization enables the device to obtain system and controlinformation during initial access and mobility procedures. The wirelessdevice then acquires fine time synchronization in a second phase. Thisfine time synchronization is essential when there is scheduled datatransmission—especially one applying modulation with high spectralefficiency—for the wireless device, in order to enable accurate channelestimation and subsequent data detection. Data detection, especially inthe cases of high-order modulation and spatial multiplexing (e.g.,MIMO), has higher requirements on channel estimation quality. Differentreference signals and/or synchronization signals are used for the twosynchronization phases. The various embodiments of the current inventiveconcept are pertinent to the fine time synchronization procedure and thecorresponding FTRS.

In NX, ultra-lean transmission is envisioned aiming to minimize thealways-on transmissions such as the CRS. In this new paradigm, thewireless device makes no assumption on a subframe's content (i.e., eachparticular signal is configurable and may thus be absent in a particularframe), unless a specific signal is scheduled in that subframe or thedevice has been instructed to expect supporting signals. This manner ofoperation has several benefits, such as (but not limited to) energyefficiency and interference minimization.

Another characteristic present in some embodiments is that transmissionsare well-confined in time and in frequency, so that dependency acrosssubframes is avoided, and the spectrum is not cluttered with signalsoutside the scheduled data transmission. This means reference signalsnecessary for channel estimation may be transmitted in the same subframeand over the same bandwidth as the data transmission.

In this approach, multi-antenna schemes become more transparent to thewireless device, and the subframe structure may be used for newservices. That is, transmission may be allocated the full availablesystem bandwidth. If new services are added, allocation of new resources(e.g., time and frequency) has to consider that some subcarriers allover the system's bandwidth are partly used (to make sure that the newservice-related signals do not overlap already allocated resources).When reference signal transmissions are confined to a time-frequency boxthe situation becomes much simpler. The embodiments described in thissection achieve a design trade-off to maintain the fundamental abilityof acquiring fine time synchronization, while maintaining a lean andfuture-proof carrier. Although the embodiments set forth in thisdocument can be used for fine time synchronization in 5G, this type ofparadigm is not the only field where the present embodiments areapplicable and useful.

A wireless device can be configured with an FTRS pattern for listeningfor the FTRS. Fine synchronization achieved using the FTRS enablessuperior timing estimation during demodulation of data received in acorresponding physical channel. In this document, the term “UE” (i.e.,user equipment) may be used as a shorthand notation for wireless device,but this notation is not intended to be limiting.

An example FTRS pattern includes a sequence of time-frequency resources,i.e. time and bandwidth limited resources that may be used fortransmitting the FTRS. In a multi-carrier system, the resourcescorrespond to the subcarriers allocated to the FTRS pattern. It isadvantageous to construct multiple orthogonal FTRS. Orthogonality may beobtained by mapping FTRS to different symbols or to differentsubcarriers (e.g. a subcarrier comb or non-overlapping bandwidth),and/or using (partly) overlapping time-frequency resources, whileensuring that orthogonality is achieved over the overlapping resourcesvia the FTRS content. Ensuring orthogonality may include applyingorthogonal cover codes or classical CDM, such as cyclically shiftedZadoff-Chu sequences. Configuration of FTRS may be done usinghigher-layer signaling such as Radio Resource Control (RRC) signaling.

The configured resources may include a time pattern (e.g. periodic) andthe FTRS may be transmitted according to this pattern. Anotherpossibility is that the configuration just specifies the resources,where FTRS may be transmitted. In this case, determination of whether totransmit FTRS may be more dynamic, as discussed later (see section“Triggering of FTRS Transmission”). If FTRS resources are specified butnot necessarily used, the UE may dynamically determine if FTRS have beensent or not (see section “Dynamic Determination whether FTRS arePresent”).

FIGS. 1 and 2 are graphical illustrations (time vertically versusfrequency horizontally) of FTRS-related resource-usage situations 100and 200. A UE (not shown in these figures) is configured to potentiallyreceive FTRS in time and frequency blocks (i.e., resources) 110, 120,130, 140 and 150, in FIG. 1, and 210, 220, 230, 240 and 250, in FIG. 2,respectively. A sequence of time-frequency resources (i.e., 110-150 or210-250) forms an FTRS pattern, which is limited in time and bandwidth.In a FTRS pattern, one time-frequency resource may consist of aplurality of resource elements which are contiguous in thetime-frequency plane. However the time-frequency resources may also bediscrete in frequency. The time-frequency resource in this patternactually used to transmit FTRS may precede or (partially) overlap thefrequency-time blocks (i.e., 175 and 275, respectively) scheduled forthe data transmission on the physical channel. The scheduledfrequency-time blocks may be bandwidth and potentially also time (ifdata volume is known) allocated for a data transmission. Accurate timingachieved based on FTRS is used for channel estimation and decoding datareceived during the data transmission.

Although plural time-frequency resources may be used for transmittingthe FTRS, the FTRS is actually transmitted using only one or few ofthese resources. In one embodiment, the FTRS pattern may be periodic andnot limited to a time interval, although the FTRS are transmittedoccasionally, in association with definite data transmission(s). In FIG.1, time-frequency resource 120 preceding the frequency-time block 175scheduled for the data transmission is used for transmitting the FTRS,while other resources of the FTRS pattern (i.e., 110, 130, 140 and 150)are not used for transmitting the FTRS. In FIG. 2, frequency-timeresource 230 overlapping the frequency-time block 275 scheduled for thedata transmission is used for transmitting the FRTS, while otherresources of the FTRS pattern (i.e., 210, 220, 240 and 250) are not usedfor transmitting the FTRS. In the latter case, the data transmission ispunctured by the FTRS transmission. Frequency-time resources of the FTRSpattern overlapping with the frequency-time block scheduled for datatransmission, but not used for the FTRS transmission (e.g., 130, 140,150, 240 and 250) are instead used for the data transmission.

Data transmission may either be punctured or rate mapped around FTRS. Inpuncturing, during channel coding, the resource loss due to FTRSresources is not considered, but the coded bits overlapping the usedFTRS resources are not transmitted. If FTRS is considered during ratematching, the code rate is slightly increased, i.e. less coded bits aregenerated which fit the data resources minus FTRS resources.

Beamforming

5G systems will often be deployed using many steerable antenna elements(e.g., using an array of independently controllable antenna elements) atleast on the base station. To reduce interference and/or improvecoverage data sent to a UE by such systems, transmissions will thereforeoften be user-specifically beamformed. For control signaling (such ashandover signaling), fixed and often wider beams are used to increaserobustness of the signaling. These different beamforming patterns can becreated by selecting different precoder weights. Transmitting FTRS usesbeamforming, sometimes purposefully matching the coverage of the FTRStransmission beam with the beam for the related data transmission on thephysical channel. However, the beamforming weights of the FTRStransmission beam don't have to be the same as the weights used in therelated data transmission on the physical channel. Using differentweights—e.g., weights creating wider beams for transmitting the FTRS—hasthe advantage that the FTRS can be used by multiple UEs. However, a widebeam pattern may not always be favored, e.g., it may fail to providesufficient coverage for the FTRS to reach the targeted UE, or due torare propagation conditions the timing obtained from FTRS transmittedwith a wide beam may not match the data transmission because differentpropagation paths are experienced for different beams. Thus, the FTRSbeam may be formed using similar or the same weights as for thecorresponding data transmission on the physical channel. Especially, ifthe beam for the corresponding data transmission on the physical channelis narrow, the FTRS beam may also only cover a single user.

Triggering an FTRS Transmission

Since, in some embodiments, FTRS are not always transmitted on theconfigured resources, the network needs to dynamically decide when totransmit FTRS. An example would be HOM or MIMO transmissions, whichtypically require accurate timing; the network may trigger an FTRStransmission when the corresponding data transmission on the physicalchannel is a HOM or a MIMO transmission.

Even if a transmission needing accurate timing is scheduled, the networkmay refrain from transmitting an FTRS if the UE has sufficientlyaccurate timing. The UE may be determined to have sufficiently accuratetiming if the FTRS has been recently transmitted (as in FIG. 1 when FTRSwas transmitted shortly before the data transmission is scheduled), ifthe block error rate (BLER) is in the expected range, or if the timingof UL transmissions from the UE arrive at the network accurately withrespect to time. The UE may also request transmissions of FTRS or reportreception quality. Reception quality may be explicitly related totiming, or at least enable the network to infer whether timing accuracyis adequate.

Dynamic Determination Whether FTRS are Present

If not all configured FTRS resources contain FTRS transmissions (i.e.,if the design of the system allows using only some of the possible FTRSresources, depending on need), the UE may be configured to determine ifFTRS is present or not. If FTRS is very wideband and/or long, it mayprovide sufficient processing gain and the UE could detect FTRS presenceblindly.

If the UE is not able to detect the presence of FTRS, according to anembodiment, the UE may receive an indication that FTRS are present orforthcoming. Such an indication may be sent in an extra bit (or bitfield if not only transmission yes/no is indicated, but a few moreparameters can be dynamically selected) in the control channelscheduling the corresponding data transmission on a physical channel(which requires the accurate timing). Some embodiments may operateaccording to an implicit (default) rule. For example, if the controlchannel schedules a data transmission requiring accurate timing (e.g.HOM, MIMO), then the overlapping/next coming/closest configuredtime-frequency resource contains an FTRS.

In another embodiment, an extra control channel message may be used toschedule FTRS. A scheduling command may be valid for the next configuredFTRS resource, or for an FTRS-configured resource in the near future, orfor a few configured FTRS resources. Since an extra control channeltypically requires a few bits such as user/group ID, the relativeadditional overhead could be acceptable to allow for somewhat moredynamic options. An interesting option is to schedule this controlchannel (and thus the FTRS) not to a single user but to a group ofusers; the control channel would in this case use a group ID.

UE Behavior

According to an embodiment, a UE configured with FTRS is able todetermine if FTRS are present in one of the FTRS pattern'sfrequency-time resources (as already discussed is section “DynamicDetermination whether FTRS are Present”). If the UE determines no FTRSis present, it assumes the FTRS pattern's frequency-time resources arenot used for FTRS. For example, if the UE has other physicalchannels/signals overlapping with the FTRS pattern's frequency-timeresources, it assumes the FTRS pattern's frequency-time resources areused for this other physical channel/signal (e.g., as 130-150 in FIG.1).

If the UE determines that FTRS is present, the UE assumes the configuredresources are not used for another physical channel/signal to bereceived by the UE. For example, if the UE receives a data transmissionon the physical channel partly overlapping with the FTRS pattern'sfrequency-time resources, the UE assumes the data transmission is notmapped to the FTRS pattern's frequency-time resources (as for 230 inFIG. 2). The data transmission on the physical channel may either bemapped around the FTRS resources (in which case it is preferably ratematched), or rate matching is not adopted and the physical channelsymbols mapped onto FTRS resources are punctured. The term “around” inthis context means that, in a time-frequency plane, the physical channelresources scheduled to be used for the data transmission are adjacentthe FTRS resources 240, 250 (e.g., on two or more sides or portions ofsides thereof). However, “around” does not require the FTRS resource besurrounded by the physical channel resources scheduled to be used forthe data transmission.

The UE uses the FTRS also to obtain more accurate timing fordemodulation of the corresponding data transmission on the physicalchannel. However, if the UE already has adequate timing accuracy, it maynot use the FTRS.

FIG. 3 is a flowchart illustrating a method 300 performed by a basestation according to an embodiment. Note that the “base station” termhere is not intended to be limiting, rather indicating a network device(e.g., an access point, a network node, etc.) as opposed to a wirelessdevice merely connected to the network. In a cloud environment, itshould be understood that different functionalities may be implementedon different physical devices. For example, the FTRS configuration maybe provided by an RRC node, the FTRS-related decisions may be formed ona base station and the actual transmission of the FTRS or transmissiondata may emerge from another distinct physical device.

At 310, the base station configures the UE with FTRS resources. At 320,the base station determines whether to transmit FTRS to the UE. Ifdetermined that FTRS should be transmitted (the Y branch of 320), the UEtransmits FTRS according to the UE's configuration, at 330. Optionally,the base station indicates the FTRS transmission to the UE at 340.

FIG. 4 is a diagram of a method 400 for a base station according to anembodiment. Method 400 includes detecting a trigger for transmitting afine timing reference signal, FTRS, related to a data transmission on aphysical channel, for a wireless device at 410. Method 400 furtherincludes transmitting the FTRS according to an FTRS pattern associatedwith the wireless device and including a sequence of time-frequencyresources at 420. In a variation of the embodiment shown in FIG. 4, thebase station may just transmit the FTRS (according to the FTRS pattern)related to a data transmission on a physical channel, and transmit thedata transmission (i.e. without an explicit trigged detection step).

The trigger for transmitting a fine timing reference signal is an actionor situation that indicates the need or a highly likelihood of the needfor the wireless device to be able to perform a fine synchronization. Indifferent embodiments, one or more of the following potential triggersmay be implemented. The trigger may be:

-   -   the data transmission being an HOM or MIMO transmission,    -   a predetermined time interval passed since FTRS has been        transmitted to the wireless device,    -   the Block Error Rate (BLER) related to the wireless device        exceeding a predetermined BLER threshold,    -   a timing accuracy (TA), of an uplink transmission from the        wireless device is less than a predetermined TA threshold,        and/or    -   an FTRS request received from the wireless device.

As already discussed, receiving these FTRS enables the wireless deviceto perform fine synchronization. The data transmission may partiallyoverlap the FTRS pattern (e.g., 110-150 and 210-250 overlapping 175 and275 in FIGS. 1 and 2). As in FIG. 2, the FTRS may be transmitted on afirst resource overlapping the scheduled data transmission on thephysical channel. The data transmission may use the FTRS pattern'sfrequency-time resources not used for transmitting FTRS. In oneembodiment, the data transmission of a physical channel may be puncturedby the FTRS pattern's frequency-time resource used to transmit the FTRS.In another embodiment, the data transmission on the physical channel ismapped around (not necessarily surrounding) the periodic pattern'sfrequency-time resources. The data transmission on the physical channelmay be rate-matched.

FIG. 5 is a schematic diagram of a base station able to perform methods300 and 400 and all other embodiments described in this document. Basestation 500 includes a network interface 510 configured to emit andreceive signals to other devices in the communication network 512.Network interface 510 is connected to a processing unit 520 configuredto control interface 510 to send FTRS signals to wireless devices,thereby enabling time synchronization thereof. Base station 500 may alsoinclude a memory 540 and a user interface 530. Memory 540 may storeexecutable codes which, when executed by processing unit 520 makeprocessing unit to perform methods according to various embodiments.

FIG. 6 is another diagram of a network node 600 according to anembodiment. The network node includes hardware and/or software modules.A detecting module 610 is configured to detect a trigger fortransmitting an FTRS related to a data transmission to a wirelessdevice, on a physical channel. A transmission module 620 is configuredto transmit the FTRS according to an FTRS pattern associated with thewireless device, the FTRS pattern including a group of time-frequencyresources.

FIG. 7 is a flowchart illustrating a method 700 performed by a wirelessdevice according to an embodiment. At 710, the wireless device receivesa FTRS pattern. At 720, the wireless device determines whether the FTRSare going to be transmitted according to the FTRS pattern. If determinedthat the FTRS have been received (the Y branch of 720), the wirelessdevice uses the received FTRS for timing adjustment (if needed) at 730.Then, at 740, the wireless device receives the data transmission on thephysical channel. However, at 750, the wireless device receives the datatransmission on the physical channel without receiving FTRS (the Nbranch of 720).

FIG. 8 is a flowchart of a method 800 for a wireless device connected toa communication network according to an embodiment. Method 800 includeslistening according to an FTRS pattern that includes a sequence oftime-frequency resources, until detecting a FTRS related to a datatransmission on a physical channel at 810. Method 800 further includesreceiving the data transmission on the physical channel at 820. Method800 may further include optionally include performing a finesynchronization using the FTRS to decode data received during the datatransmission.

As exemplarily illustrated in FIGS. 1 and 2, the data transmission asscheduled may partially overlap the FTRS pattern. As in FIG. 1, the FTRSmay be detected on one of the frequency-time resources in the FTRSpattern, prior to the data transmission. Alternatively or additionally,as in FIG. 2, the FTRS may be detected on a first of the time-frequencyresources in the FTRS overlapping the data transmission as scheduled.The data transmission may use some of the overlapping time-frequencyresources in the FTRS pattern that are not used for transmitting theFTRS.

In some embodiments, the wireless device starts listening following anFTRS trigger. The FTRS trigger may be receiving an indication from thecommunication network. The FTRS trigger may be receiving data afterlonger than a predetermined time interval passed (and thus potentiallythe fine synchronization has been lost). Alternatively, the FTRS triggeris the wireless device submitting a request for FTRS upon receiving adata transmission. Alternatively or additionally, the FTRS trigger maybe the data transmission, which is a HMO or a MIMO transmission, beingscheduled.

In one embodiment, the data transmission received on the physicalchannel is punctured by one or more of the time-frequency resources inthe FTRS pattern on which the FTRS is detected. In another embodiment,the data transmission received on the physical channel is mapped aroundone or more of the time-frequency resources in the FTRS pattern on whichthe FTRS is detected.

Method 800 may also include receiving FTRS configuration data fordetermining the FTRS pattern. The time-frequency resources in the FTRSpattern may include less than a bandwidth configurable for communicationbetween the wireless device and the communication network. Thetime-frequency resources in the FTRS pattern may be at equal timeintervals and/or may cover same frequencies.

FIG. 9 is a schematic diagram of a wireless device able to performmethods 700 and 800 and all other embodiments described in thisdocument. Wireless device 900 includes a network interface 910configured to emit and receive signals to other devices in thecommunication network 912. Network interface 910 is connected to aprocessing unit 920 configured to control interface 910 to receive FTRSsignals, thereby enabling time synchronization based on the receivedFTRS and/or data reception on the corresponding channel.

Wireless device 900 may also include a memory 940 and a user interface930. Memory 940 may store executable codes which, when executed byprocessing unit 920 make the processing unit perform methods accordingto various embodiments.

FIG. 10 is another diagram of a wireless device 1000 including hardwareand/or software modules according to an embodiment. A listening module1010 is configured to listen, according to an FTRS pattern that includesa group of time-frequency resources, until detecting an FTRS related toa data transmission on a physical channel. A data receiving module 1020is configured to receive the data transmission.

To summarize, according to several embodiments a wireless deviceconnected to a network is configured to receive FTRS enabling accuratesynchronization for a data transmission on a physical channel. The FTRSand the physical channel are quasi-co-located with respect to timeand/or frequency. The time-frequency resources used to transmit the FTRSare pre-configured in an FTRS pattern. The wireless device uses the FTRSfor decoding the data transmission on the physical channel. The FTRS maybe emitted by the network using a beam defined for the wireless device.Presence of the FTRS may be indicated to the wireless device via anextra bit in a control channel. FTRS configuration may contain atime-frequency pattern of when and where (frequency-wise) to expectFTRS. The wireless device may determine the presence of FTRS blindly.

Transmitting the FTRS occasionally (on demand or when needed) leads tomore energy-efficient network operation than conventional methods (e.g.,when continuously transmitting the CRS). Moreover using less than theentire available bandwidth to transmit these fine synchronizationsignals leaves room (bandwidth) for additional signals and services.

It should be understood that this description is not intended to limitthe invention. On the contrary, the exemplary embodiments are intendedto cover alternatives, modifications and equivalents, which are includedin the spirit and scope of the invention. Further, in the detaileddescription of the exemplary embodiments, numerous specific details areset forth in order to provide a comprehensive understanding of theinvention. However, one skilled in the art would understand that variousembodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodimentsare described in the embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the embodiments or in various combinations with or withoutother features and elements disclosed herein. The methods or flowchartsprovided in the present application may be implemented in a computerprogram, software or firmware tangibly embodied in a computer-readablestorage medium for execution by a computer or a processor.

This written description uses examples of the subject matter disclosedto enable any person skilled in the art to practice the same, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the subject matter is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims.

What is claimed is:
 1. A method implemented in a wireless device, themethod comprising: receiving, by the wireless device, an indication ofphysical channel resources; and detecting, by the wireless device, areference signal quasi-co-located with the indicated physical channelresources.
 2. The method of claim 1, further comprising performing, bythe wireless device, a timing estimate for data transmission on theindicated physical channel resources.
 3. The method of claim 2, whereina demodulation of the physical channel resources overlaps the timingestimate.
 4. The method of claim 1, further comprising performing, bythe wireless device, channel measurements based on the receivedreference signal and following a reference signal trigger.
 5. The methodof claim 4, wherein the reference signal trigger is an indicationreceived from a communication network.
 6. The method of claim 1, furthercomprising receiving, by the wireless device, a reference signalconfiguration data for the reference signal.
 7. The method of claim 1,wherein the reference signal corresponds to time and frequency resourceswhich are less than a bandwidth configurable for communication betweenthe wireless device and the communication network.
 8. The method ofclaim 1, wherein the reference signal corresponds to one or moretime-frequency resources in a reference signal pattern which are atequal time intervals and/or cover same frequencies.
 9. The method ofclaim 1, further comprising performing, by the wireless device, a finesynchronization using the reference signal to decode data receivedduring data transmission.
 10. A wireless device comprising processingcircuitry operable to: receive, by the wireless device, an indication ofphysical channel resources; and detect, by the wireless device, areference signal quasi-co-located with the indicated physical channelresources.
 11. The method of claim 1, wherein the reference signal andthe indicated physical channel resources are quasi-co-located in timeand/or frequency.